Field
The disclosed concept relates to vacuum switching apparatus such as, for example, vacuum switches including a vacuum envelope such as, for example, vacuum interrupters. The disclosed concept also pertains to electrical contacts for vacuum interrupters.
Background Information
Vacuum interrupters include separable main contacts located within an insulated and hermetically sealed vacuum chamber. The vacuum chamber typically includes, for example and without limitation, a number of sections of ceramics (e.g., without limitation, a number of tubular ceramic portions) for electrical insulation capped by a number of end members (e.g., without limitation, metal components, such as metal end plates; end caps; seal cups) to form an envelope in which a partial vacuum may be drawn. The example ceramic section is typically cylindrical; however, other suitable cross-sectional shapes may be used. Two end members are typically employed. Where there are multiple ceramic sections, an internal center shield is disposed between the example ceramic sections.
Some known vacuum interrupters include a radial magnetic field generating mechanism such as, for example and without limitation, a spiral electrical contact or a contrate cup, designed to force rotation of the arc column between the pair of electrical contacts interrupting a high current, thereby spreading the arcing duty over a relatively wide area. These vacuum interrupters suffer from a number of disadvantages. For example, as the electrical contacts experience repeated interruption of relatively high fault currents, the individual petals of the electrical contact begin to “bridge.” More specifically, the individual petals of the electrical contact begin their life spaced apart from each other by slots that force the arc column to spread over the contact. As the electrical contact experiences repeated interruption of relatively high fault currents, the heavy columnar arcing causes the metal of the electrical contact to melt such that the spacing between the petals decreases, and is eventually bridged. As a result, the bridged electrical contact is prevented from allowing the arcing duty to spread over a relatively wide area. Thus, the bridged electrical contact results in the arcing being localized in the center of the electrical contact. This undesirably shortens the life of the electrical contact due to the inability to adequately interrupt the relatively high fault currents.
There is thus room for improvement in vacuum switching apparatus and in electrical contacts therefor.